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A superconducting cable system in which at least one superconducting
electrical cable is arranged in a cryostat which consists of two metallic
tubes, which are arranged concentrically and at a distance from one
another. Vacuum insulation is fitted in the circumferential gap formed by
the distance between the tubes, which vacuum insulation consists of
spaces composed of a material having low thermal conductivity and plastic
films coated with a metal and having high reflectivity. The gap is
evacuated. In addition, thermally insulating material (9) is arranged in
the gap, and its thermally insulating characteristics are independent of
the vacuum which is produced between the two tubes (5, 6).

1. Superconducting cable system, comprising: at least one superconducting
electrical cable is arranged in a cryostat which has two metallic tubes,
which are arranged concentrically and at a distance from one another and
in which vacuum insulation is fitted in the circumferential gap formed by
the distance between the tubes, which vacuum insulation has spaces
composed of a material having low thermal conductivity and of plastic
films coated with a metal and having high reflectivity, and in which the
gap is evacuated, wherein thermally insulating material is additionally
arranged in the gap between the two tubes, where said insulating
material's thermally insulating characteristics are independent of the
vacuum which is produced between the two tubes.

2. Cable system according to claim 1, wherein the vacuum insulation
panels are used as the thermally insulating material.

3. Cable system according to claim 1, wherein polyurethane is used as the
thermally insulating material.

Description

RELATED APPLICATION

[0001] This application claims the benefit of priority from European
Patent Application No. 09 306 240.4, filed on Dec. 16, 2009, the entirety
of which are incorporated by reference.

BACKGROUND

[0002] 1. Field of the Invention

[0003] The invention relates to a superconducting cable system.

[0004] 2. Description of Related Art

[0005] One such cable system is described in EP 0 326 923 B1.

[0006] In a cable system such as this, the cryostat is used as a sheath
for the at least one superconducting electrical cable and the connecting
areas thereof in end terminations. The aim is to ensure that the
temperature of the cryogenic medium carried therein is maintained in the
long term, and over relatively long distances as well, without
significant heating. One such medium is, for example, nitrogen which, for
example, is introduced into the cryostat at a temperature between 67 K
and 90 K.

[0007] According to the initially cited EP 0 326 923 B1, the cryostat
consists of two tubes, which enclose a gap between them, are composed of
stainless steel, and can also be corrugated transversely with respect to
their longitudinal direction, in which gap spaces composed of a material
having low thermal conductivity and of plastic films coated with a metal
and having high reflectivity are arranged between the two tubes, which
spaces reduce the radiated heat. The gap is also evacuated. As long as
the vacuum exists, a cryostat such as this can carry out its functions.
However, if it collapses, for example as a result of damage to the outer
tube of the cryostat, a sufficient amount of heat is introduced into the
cryostat such that the operational reliability of the cable system is no
longer ensured. The superconducting cable must then be disconnected
immediately from the power supply system in order to prevent an
electrical flashover from occurring in the cable system, because gas
bubbles are formed in the cooling medium, in particular in nitrogen,
because of the heat that is introduced. A flashover such as this would
lead to destruction of parts of the cable system. This would lead to
considerable damage, particularly in an end termination. The
superconducting cable cannot be used again until the cryostat has been
repaired. This requires a correspondingly large amount of effort.

OBJECTS AND SUMMARY

[0008] The invention is based on the object of designing the initially
described cable system such that it can continue to operate even when the
cryostat is damaged.

[0009] The additional thermally insulating material ensures that, if the
vacuum in the cryostat collapses, the heat which is introduced into the
cable system is sufficiently little that it is still possible initially
to continue to operate it reliably. The risk of destruction of the cable
system by an electrical flashover is precluded, in particular because no
gas bubbles are formed in the cooling medium. Sufficient time remains to
switch the power transmission to a different path, before the
superconducting cable is disconnected from the power supply system.

[0010] By way of example, suitable thermally insulating materials are
polyurethane and, in particular, vacuum insulation panels which contain a
highly porous, thermally insulating material which is surrounded in a
hermetically sealed form by a film, and the space surrounded by the film
is evacuated. By way of example, one such material is silicic acid.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] One exemplary embodiment of the subject matter according to the
invention is illustrated in the drawings, in which:

[0012] FIG. 1 shows a schematic illustration of a superconducting cable
system according to the invention.

[0013] FIG. 2 shows a cross section through an enlarged illustration of a
cryostat used in the cable system.

DETAILED DESCRIPTION:

[0014] The cable system which is illustrated schematically in FIG. 1 has
two end terminations 1 and 2, between which a superconducting cable 3 is
arranged. In the end terminations 1 and 2, the cable 3 can be connected
to a superconducting cable, which continues further, or to a normally
conductive cable, or via an appropriately designed bushing to an
electrical device. The configuration of the superconducting cable 3 and
its electrical connection to parts which continue further are not of
importance here. They will therefore not be described in anymore detail.

[0015] The superconducting cable 3 and the two end terminations 1 and 2
are surrounded by a cryostat KR whose design is shown, for example, in
FIG. 2. By way of example, a cooling medium, which is present in a supply
area 4, is fed into the cryostat KR, for example nitrogen, by means of
which the superconducting conductor in the cable 3 is changed to the
superconducting state, and is maintained in this state. This is ensured
by the cryostat KR, in which the cable is accommodated on the path
between the two end terminations 1 and 2. Two or more superconducting
cables could also be arranged in the cryostat KR.

[0016] The cryostat KR consists of two metallic tubes 5 and 6 which are
arranged concentrically at a distance from one another and between which
there is a circumferential gap. The two tubes 5 and 6 are advantageously
composed of stainless steel. They may also be corrugated transversely
with respect to their longitudinal direction. A space 7, which is
composed of a poorly thermally conductive material, is fitted in the gap
between the two tubes 5 and 6 and holds the two tubes 5 and 6
concentrically with respect to one another over their entire length. The
space 7 is advantageously in the form of a strand, which is arranged with
a helical profile between the two tubes 5 and 6. It may also be designed
differently, provided that the design ensures that thermally insulating
material can be fitted without any gaps in the gap between the two tubes
5 and 6.

[0017] When the cryostat KR is fully functional, so-called superinsulation
8 is fitted in the gap between the two tubes 5 and 6, composed, for
example, of plastic films coated with metal, for example aluminium, and
in each case with non-woven material located between them. The
superinsulation 8 is indicated in FIG. 2 by dashed lines running in a
circular shape. The gap between the two tubes 5 and 6 is also evacuated.

[0018] In addition to the superinsulation 8, thermally insulating material
9 which is identified by the crosses drawn in FIG. 2, is fitted in the
gap between the two tubes 5 and 6. There are no gaps in the insulating
material 9 in the gap between the two tubes 5 and 6, and it largely fills
this gap, together with the films of the superinsulation 8. It can be
arranged above the superinsulation 8 or between the layers thereof. The
insulating material 9 is advantageously located underneath the
superinsulation 8, as is shown in FIG. 2.

[0019] By way of example, Polyurethane or some other known thermally
insulating materials can be used as the thermally insulating material 9.
However, in one preferred embodiment, a highly porous material, such as
silicic acid, is used, which is surrounded in a hermetically sealed
manner by a film in a vacuum insulation panel, with the area which the
film surrounds being evacuated. This vacuum is independent of the vacuum
which exists in the gap between the two tubes 5 and 6. The vacuum is
therefore maintained even if the vacuum in the gap collapses. The
thermally insulating material 9 retains its characteristic even when the
vacuum collapses, as a result of which the area surrounded by the
cryostat KR is protected against sudden introduction of heat.